January 26, 1976 12:00 PM

In a corner of Prof. James H. Williams’ third-floor office overlooking the MIT campus in Cambridge, Mass. sits a bizarre scientific instrument. A perpetual-motion machine? The ultimate computer? Nothing so trivial. It is a monstrous 27-inch yo-yo, and any visitor is advised to show proper respect, because Williams and MIT take it seriously.

Williams, 34, an associate professor of mechanical engineering, was showing the yo-yo the other day to a troop of high school kids, the most recent in a constant parade of curious pilgrims. Williams was offered $5,000 for the yo-yo by a Las Vegas casino (“I feel sensitive about selling it”), and laughed off suggestions that he drop it from Canada’s tallest structure, Toronto’s 1,800-foot Canadian National Tower. “There were all sorts of radio and TV offers,” he says wearily.

Williams constructed the yo-yo two years ago in a between-semesters special course. Ten students signed up. Explained one of them, “How could I pass up the chance of a lifetime?”

When the 35-pound contraption, made of two bicycle wheels, was ready, Williams took it to the roof of a 21-story building at MIT. He anchored the cord to an I beam, hooked up a motor which jerked the line rhythmically like a finger and let the yo-yo drop. The wheels, revolving up to 1,000 times a minute, reached a speed of more than 80 miles an hour. Then, the yo-yo climbed more than two-thirds of the way back up the 400-pound-test-weight nylon cord.

The scientific principle involved, according to Williams, is the conversion of the potential energy of a poised yoyo into kinetic energy and vice-versa. “I am interested in the dynamics of toys,” says Williams, “because they have lots of subtle and sophisticated aspects in a kinetic sense. Besides, too many technical people cultivate their gardens too tightly.”

After high school, Williams himself worked as a machinist in a shipbuilding yard in his native Newport News, Va. Then he went back to school and has earned two MIT degrees, a Cambridge doctorate and an award for outstanding undergraduate teaching. He lives with his wife, Karen, a poet, and his 5-year-old son, “J.T.,” in an MIT dorm where he is the house master. He is an intramural football and basketball player and a flutist.

Williams’ inspired students now want to build a giant Frisbee and sail it across the Charles River with, yoicks, the professor aboard. “It’s too dangerous,” he says with the prudence of advancing years and approaching tenure. This month, between semesters, Williams is offering a cooking course.

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